In the field of metal packaging, typical containers are sealed by seaming a can end onto a can body using the well-known double seaming process. The double seaming process is typically performed on a seaming machine having a plurality of forming stations. Each station contains a rotatable seaming chuck that acts as an anvil to support the can end while two rotatable seaming rolls are brought into contact with the container using a cam motion. The two seaming rolls define specific groove geometries that are configured to form a portion of the can body and a portion of the can end into a commercially acceptable double seam.
A can body is typically raised into engagement with a forming station using a lifter plate or other positioning mechanism. After the double seam is formed and the positioning mechanism is retracted, the sealed container is ejected from the station so the seam-forming cycle can be repeated on another container. Typically, ejection of the seamed container may be achieved by the use of a knockout rod or pad that taps the center of the container to knock the container out of engagement the seaming chuck.
A trend in beverage cans has been toward reduced end diameters. Further, many conventional beverage can ends have a small center panel diameter relative to a seaming panel or peripheral curl diameter. For example, U.S. Pat. Nos. 6,065,634, 6,702,142, 6,516,968 and 7,350,392, each of which is incorporated by reference in its entirety, disclose beverage can ends having a relatively small center panel because the chuck wall is inclined (as measured from an upper point to a lower point of the chuck wall).
The conventional design of knockout pad and seaming chuck is such that the seaming chuck locates the can end. Thus, conventional knockout pads typically fit inside the diameter of the surface of the chuck that contacts the can end, which leaves a certain amount of radial movement between the can end and the knockout prior to engagement with the seaming chuck. With certain end designs (i.e. lightweight ends) the countersink is moved inboard and with the traditional design of knockout, the radial movement available to the can end prior to engagement with the seaming chuck is increased. This radial movement is a result of the knockout not having a feature that locates and controls the end concentric with the rotatable seaming chuck. With this radial movement comes the opportunity for misalignment on assembly with the seaming chuck (during what's called the transition zone) which may cause collapse, creases and poor seam quality.
Furthermore, after conventional knockouts have located a can end, the load applied to the can end decreases to zero during the transition zone. Therefore, by the time the can body and can end engage the chuck, the can end and can body combination could be misaligned to the chuck, thereby causing damage to the can bodies and can ends. To prevent damage, often times certain seamers have to run at slower speeds such as less than 1500 cans/minute.
Accordingly, there is a need for an improved apparatus and method for locating and seaming a can end onto a can body.